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  • 2010-2014  (2)
  • 1980-1984  (1)
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  • 1
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    Avalanche grainflow on a simulated aeolian dune (2013)
    Wiley
    Details
    Publication Date: 2013-08-17
    Description: [1]  Avalanches maintain the slipface of aeolian dunes, which alters their air flow characteristics and sediment dynamics, and results in the development of grainflow cross-bedding. We report on a series of experiments in which avalanches were observed on a 1:1 replica of a small (1.2 m brink height) transverse dune in the Dune Simulation Wind Tunnel (DSWT) under wind velocities of 8-11 m s −1 . Changes in slipface topography were observed photographically and measured utilizing a 3D laser scanner with 1 mm 2 spatial resolution. Avalanches in non-cohesive sands were observed to progress through scarp recession from the point of initiation and continue until the slope angle is reduced. Changes in local slope confirm that the steep, pre-avalanche mean slope relaxes to a uniform value equal to the angle of repose of the test sand (32°) over all involved portions of the slipface. Avalanche volumes are measured, and demonstrate that avalanche magnitude is independent of windspeed over the range of velocities observed. This independence provides the potential to significantly simplify the modelling of grainflow as a function of only the total cross brink sediment transport.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Lee slope sediment processes leading to avalanche initiation on an aeolian dune (2013)
    Wiley
    Details
    Publication Date: 2013-08-17
    Description: [1]  In order to detail the governing conditions through which a slipface matures to the point of failure, dry sand avalanches were observed in the Dune Simulation Wind Tunnel (DSWT) on a 1:1 replica transverse dune with a crest height of approximately 1.2 m. Areal distributions of grainfall and reptation were measured using traps. Changes in the slipface elevation were observed using 3D laser scanning with a vertical accuracy of 0.096 mm for approximately every 1 mm 2 of surface area. Grainfall decayed exponentially from the brink with a constant rate across all wind velocities. Reptation removed sediment from areas close to the brink, and deposited it downslope, creating low amplitude, cross-slope ripples on the slipface. A critical length scale separating grainscale and bulk sediment behaviour is identified, and it defines the lower limit to the validity of angle of repose measurements. Avalanche initiation occurred in an area of steep surface slope below a sediment bulge, with distance from the brink independent of wind velocity. The time between avalanches was found to be constant for constant wind velocity.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Electronic Resource
    Electronic Resource
    Relative effectiveness of vitamin D metabolites in increasing bone mineral solubility (1981)
    Springer
    Calcified tissue international 33 (1981), S. 159-165 
    Details
    ISSN: 1432-0827
    Keywords: Vitamin D metabolites ; Calcium fluxes ; Bone mineral solubility ; Mineral homeostasis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Weanling rats were given a vitamin D-deficient diet containing 1.4% calcium and 1.0% phosphorus. After 4 weeks these deficient animals were injected for 7 days with selected doses of one of the following vitamin D metabolites: 25(OH)D3, 1,25(OH)2D3, 24,25(OH)2D3, 25,26(OH)2D3 or the ethanol vehicle. A vitamin D-replete group was placed on the same diet but injected with 50 IU of vitamin D3 once a week for the entire 5-week period. By the use of a modified Ussing chamber [1], the measurements of calcium fluxes into and from the rat calvaria were possible. These data enabled the apparent mineral solubilities to be derived. After 5 weeks on this diet the vitamin D-deficient rats had low levels of serum calcium (1.41 mM) and decreased mineral solubility when compared to the vitamin D-replete group. The apparent solubility of the bone mineral increased toward the vitamin D-replete level in calvaria from vitamin D metabolite-treated rats. However, these changes did not directly reflect the alterations in the level of serum calcium. At any given dose level, 1,25(OH)2D3 was the most effective metabolite in increasing serum calcium. In fact, the high dose (250 pmoles/day) was hypercalcemic. Next in effectiveness was 25(OH)D3. These two metabolites were equally effective in increasing mineral solubility. At a 10 times higher dose, the 24,25(OH)2D3 metabolite was able to normalize serum calcium and improve but not normalize mineral solubility. At the high dose (260 pmoles/day), the 25,26(OH)2D3 metabolite caused no effect on mineral solubility and minimal increases in serum calcium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02409429
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